Pressure tappings

[varnish]

Hey Guys.

I built a bench roughly following this design last year:
http://www.dtec.net.au/Flowbench%20Design%20Guide.htm

I've never been happy with it, and wanted to build a new one over this summer, still using water manometers.
I've seen (on here) a design which uses a table over the top of the orifice plate, which I will employ in my new bench.

Question is; where should I be mounting my pressure tapping's?

In the old bench they look like this.


I'm not convinced that this is accurate.

I was thinking of using tubing like an annubar, and wrapping it around the legs of the table in a circle.

Thoughts?

Any pictures of your set ups would be cool.

Varnish

[varnish]

Bump

Someone must have an idea on this....come on guys.

[jfholm]

You need pressure taps for the inclined manometer to measure pressure differential. So you need on pressure tap above the measuring orifice and one below. Just put them even with the cabinet wall on the inside of the measuring chambers. The pressure tap to measure your test pressure is just under the piece being tested. Once again mine is in the corner of the upper chamber just even with the inner wall.

John

[varnish]

I've been doing some research into pressure recovery lately.
And I think there has to be a better way of finding a position for the tappings.

This links gives 3 positions for mounting pressure tappings:
http://www.engineeringtoolbox.com/orifi ... d_590.html

But it's only concerned with orifice plates in pipe systems. So its not particularly valid in our case.

I think mounting the tappings as close to the plate as possible has to be the best way.
I think that means not against the wall, but maybe floating near the orifice, like below:


Using a y-piece to connect an annubar to the manometer. It'd just be some pvc pipe with holes drilled into it

I've also been experimenting with pressure tappings across the test piece. I have use of a blue flow bench at college.
I have connected a manometer to the top of the bore adaptor.
When I run the bench at 10" I see 12" on the manometer connected to the bore adaptor.

So the position of these tappings will make a difference.

I guess this is why I see pressures above test pressure when using the pitot tubes.
And also how I can get discharge coefficient in the 90% region.

The pressure drop isn't being measured at the restriction, but at the bottom of the bore adaptor where some of the pressure has recovered.

[1960FL]

You want your taps to be in an area with the least possability of air movement thus preventing false readings do to impact pressure. I like to think of it as in the case of the DP taps two static pickup points on each side of the orifice plate.

Rick

[Brucepts]

Here are some pics of the pickups used in the PTS Style flowbench

[Tony]

You want your taps to be in an area with the least possability of air movement thus preventing false readings do to impact pressure. I like to think of it as in the case of the DP taps two static pickup points on each side of the orifice plate.

Rick

I agree, you want to place your pickup where the air velocity is lowest, the most obvious place is right in a corner. Averaging several different pickup points is also not a bad idea.

[varnish]

That makes sense.
Cheers Guys.